Some surprise while "dd-ing" a video DVD...

[Andrea Giuliano]

Hi!

I'm doing some practice with video DVDs, and after some experiments I'm 
now able to make divx with dvd::rip, or even with transcode without 
serious problems. I post this just because I was curious about the ways 
to dump video DVDs on hard disk at a lower level, and I ran across some 
strange behaviour I cannot explain by myself.

I know that a video DVD has an ISO9660 filesystem, just like any data 
DVD or CD (if I'm not wrong). So I thought I could create an ISO image 
of a video DVD using "dd" or "readcd", for instance.

But "dd" issues an "input/output error" after a few seconds, and so does 
"readcd". I thought this could be due to the encryption used on video 
DVDs, but Nautilus can mount video DVD without problems, how can it do that?

Then, the solution came by itself: I just viewed a few seconds of the 
DVD with "mplayer", then tried again with "dd" and... voilà, "dd" goes 
on and on till all the ISO image is copied on my hard drive (a few hours 
later...). I did all the above absolutely without any intention, I just 
noticed that it worked!

What did "mplayer" do that allowed "dd" to work?

You have to know that:
1) all this happens with several different video DVDs;
2) the DVD drive is rather new (August 2005);
3) the disks work perfectly on my DVD player (I mean, they are original, 
not copies, they are clean, they have no scratches, and so on)
4) I run Breezy, updated.

Best regards.

-- 
Andrea Giuliano, Ph. D.
ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302